NASA recently repurposed a satellite called WISE that had completed its mission with all instruments intact and quite a bit of fuel. Renaming the mission NEOWISE, the space agency gave the satellite a new job: map the entire volume of space in the vicinity of Earth's orbit around the sun, looking for every possible rock, boulder, or planetoid that could possibly smack into our Blue Marble. What they discovered caused them to build an entirely new model of the space debris in our immediate area (see image above).

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What scientists found when they pored over the NEOWISE data was surprising — there were many fewer rocks floating out there than they expected to find. Dubbed "near-Earth objects," or NEOs, these potential meteorites are considered among the most dangerous threats to the planet from space. Indeed, it's likely that an NEO colliding with Earth contributed to the extinction of the dinosaurs, so it's imperative that scientists know where all of our current NEOs are.

90 percent of NEOs have now been mapped, which means that astronomers can keep an eye on them to be sure none are about to start hurtling towards us. NASA reports:

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country" . . . It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.